This invention relates to gas compressors for supplying compressed gas and in particular to compressors for supplying compressed air or other gas turbine plants for the generation of electricity.
Compressors for producing hot compressed gas, such as air for burning with fuel in the combustion chamber of a gas turbine are well known. The gas produced by the compressor is heated as it is compressed by the adiabatic nature of the compression cycle. Because the gas is heated during compression, more energy is required to achieve the desired compression than if the temperature of the gas during compression was maintained constant, i.e. if the gas was compressed isothermally. It is also generally inefficient to use the mechanical energy of the compressor to heat the body of gas being compressed.
One example of a known apparatus designed to compress gas more efficiently is the hydraulic gas compressor in which gas is compressed in a downward moving column of liquid. The gas which is in the form of bubbles is cooled by the liquid during compression. The gas is then separated from the liquid at the bottom of the column where it is conveniently stored providing a supply of cool compressed gas which may subsequently be used for power generation.
A heat engine whose operation is based on the Carnot cycle is described in U.S. Pat. No. 3,608,311. Isothermal compression of the working fluid in the cycle is achieved by spraying a liquid into the chamber containing the working fluid so that the temperature of the gas is maintained constant during compression. However, this apparatus relates to heat engines and consists of a closed cycle heat engine in which each volume of working fluid remains permanently within a respective chamber. It is not concerned with gas compressors, which supply compressed gas.
In conventional gas turbine plants the exhaust gas from the gas turbine is generally much hotter than the ambient temperature of the surrounding atmosphere so that the excess heat of the exhaust gas may be wasted unless it can be converted back into useful energy for example to generate electricity. In one particular type of gas turbine plant, the combined-cycle gas turbine and steam plant (CCGT), the excess heat in the exhaust gas from the gas turbine is converted into steam to drive a second turbine. Although the CCGT is efficient, it does require additional plant such as a heat recovery steam generator and an associated steam turbine.
According to one aspect of the present invention there is provided a gas compressor comprising a chamber to contain gas to be compressed, a piston in the chamber and means to drive the piston into the chamber to compress the gas, means to form a spray of liquid in the chamber to cool the gas on compression therein, and valve means to allow compressed gas to be drawn from the chamber, wherein said means to drive the piston comprises means to deliver driving energy stored in a fluid directly to the piston.
Thus, the invention provides a useful source of compressed gas, in which the gas temperature is controlled by the liquid spray. The heat of compression is transferred to the droplets in the spray so that during compression, the gas temperature may be controlled to remain constant or to decrease. If the temperature of the gas is held constant, the energy required for compression is much less than it is if the temperature is allowed to rise. Advantageously, the piston is driven directly by the energy stored in a fluid, which may be the energy stored in a compressed gas or a combustible fuel/air mixture or the potential energy of a liquid. This enables the isothermal compression to be driven directly from a very high temperature heat source, while heat in the system is rejected at the lowest temperatures in the cycle. The piston enables large energies released from the fluid to be very efficiently converted into compression energy of the gas, and provides the opportunity of temporarily storing the energy released from the fluid as kinetic energy in such a way that large energies can be transferred to the piston, and therefore large volumes of gas can be compressed, but the rate at which the piston moves into the chamber can be controlled by the inertia of the piston so that the compression process is as near isothermal as possible. The invention also provides the opportunity of recovering excess heat released from the fluid to preheat the isothermally compressed gas. Furthermore, because the piston is driven directly, more complex mechanical arrangements involving rotating parts such as crankshafts are not required.
In a preferred embodiment, the compressor comprises kinetic energy storage means coupled to the piston and to which sufficient kinetic energy can be imparted to enable the piston to compress the gas. Advantageously, the kinetic energy storage means may comprise a mass arranged to move in phase with the piston, and in a preferred embodiment the mass may be provided by the piston itself. Advantageously, the kinetic energy storage means may have a large inertia to control the rate of compression to allow sufficient time for the heat of compression to be transferred to the spray so that the compression is isothermal. The kinetic energy storage means may comprise a rotatably mounted mass, e.g. a fly wheel, which is coupled to the piston so that rotational energy of the mass is converted into compression energy of the gas by the piston. The rotatable mass may be arranged to reverse direction with the piston or to rotate in one direction only, independently of the direction of movement of the piston. In the former case, the piston may be mounted on a rotatable disc, movement of the piston into the chamber being along an arc produced by rotation of the disc or along a linear path, with the piston being allowed to swivel relative to the disc.
Alternatively, a rack may be connected to the piston, the rack being arranged to drive a pinion, which either provides the rotating mass or to which a rotating mass is connected. In the latter case, the piston may be coupled to the rotating mass via a crankshaft. Advantageously, the compressor may include coupling means coupled to the piston to enable power to be drawn from or supplied to the piston directly. An output drive from the piston may be used to drive, for example, valves and liquid spray injection pumps associated with the compressor and mechanical compressors, supplying hot compressed gas to drive the compressor. Power from the piston may be extracted via any suitable mechanical coupling.
In a preferred embodiment, the compressor comprises means to impart kinetic energy to the kinetic energy storage means. If the kinetic energy storage means is provided by the mass of the piston, then the means to impart may be arranged to impart kinetic energy directly to the piston. The compressor may comprise means to convert the kinetic energy used to impart movement to the piston in one direction into kinetic energy to impart movemement to the piston in the other direction. The means to convert enables, for example, kinetic energy to be imparted to the kinetic energy storage means such that the piston moves out of the compression chamber and subsequently such that the piston moves into the compression chamber to compress the gas. Alternatively, the means to convert may be used to convert some of the kinetic energy used to drive the piston into the chamber to compress the gas, to drive the piston in the other direction out of the chamber. The means to convert may include means to convert the kinetic energy used to impart movement to the piston into potential energy. For example, the kinetic energy may be converted into potential energy by arranging a mass to displace vertically on movement of the piston. This could be a separate mass or the mass could be provided by the piston itself.
In a preferred embodiment, the compressor comprises a second chamber and a second piston, each arranged such that on movement of the piston into the chamber, the second piston moves out of the second chamber. The first and second pistons may be indirectly mechanically coupled together, for example by a crankshaft. Such coupling may be adapted to preset the relative phasing of the pistons to any phase angle. Alternatively, the first and second pistons may be directly connected together and may comprise a unitary body, i.e. be formed as a single piston. The kinetic energy storage means may be provided by the mass of the second piston either alone or jointly with the mass of the first piston.
In one embodiment, the means to convert includes a body of gas contained in the second chamber. Thus, the kinetic energy stored, for example in the mass of the first and second pistons may be absorbed by the adiabatic compression of the gas in the second chamber and then allowing the relatively hot compressed gas to expand adiabatically to impart kinetic energy to the pistons in the other direction, driving the first piston into the first chamber to compress the gas therein.
In one embodiment, the gas compressor comprises containing means for containing a body of liquid and including a conduit forming the piston. The containing means may be formed as a generally U-shaped conduit with the chamber formed in one arm of the conduit and the second chamber (if there is one) formed in the other arm. Advantageously, the liquid in the liquid piston makes a perfect seal between the piston and the walls of the chamber. This form of compressor may include a piston comprising a solid material arranged in the conduit between the liquid piston and the chamber. Another piston comprising a solid material may also be arranged in the conduit on the other side of the liquid piston away from the chamber. Each of the solid pistons may have a greater density than the liquid in the liquid piston, so that, advantageously, the size of the composite piston comprising the solid and liquid components can be reduced for a given mass. Furthermore, the use of solid pistons above the liquid piston prevent direct contact between the liquid and gas and these parts of the chamber which may be relatively hot. Solid pistons also prevent interfacial disturbances at the liquid surface and the entrainment of liquid into the gas.
In another embodiment, the piston comprises a solid material and may in its construction include a number of different solid materials and may enclose, as part of its bulk mass, a liquid material. The piston and the chamber may be arranged such that movement of the piston into the chamber is in a substantially vertical plane or in a substantially horizontal plane. In the latter arrangement, low friction bearing means may be provided to support the piston to facilitate movement of the piston relative to the chamber. Advantageously, if the piston is arranged to move vertically and linearly, no bearing means may be required. Alternative arrangements in which the piston moves in other planes are also contemplated.
In one embodiment, the means to deliver driving energy comprises second valve means operable to admit hot compressed gas into the second chamber to drive the second piston out of the second chamber. Thus, if the hot compressed gas is allowed to expand adiabatically, most of the energy of the gas will be transferred to the kinetic energy storage means, which may be provided by the mass of the first and second pistons, the stored kinetic energy then being used to achieve isothermal compression of the gas in the first chamber. Since the energy released by the expansion of hot compressed gas is greater than the energy required to achieve isothermal compression of that gas, the mass of gas compressed in the first chamber can be greater than the mass of hot gas expanded in the second chamber. The kinetic energy storage means enables the energy released by the expansion of hot compressed gas to be used for isothermal compression of gas in a thermodynamically efficient way. After compression of gas in the first chamber the expanded gas in the second chamber may subsequently be compressed by driving the second piston into the second chamber. This may be achieved for example in a vertical arrangement by allowing the piston to fall under its own weight.
The compressor may include third valve means operable after compression of gas in the second chamber by movement of the piston into the second chamber, to allow compressed gas to be drawn from the second chamber. Preferably, in this embodiment, the compressor includes means to form a spray of liquid in the second chamber to cool the gas during compression. Thus, the hot compressed gas introduced into the second chamber and allowed to expand adiabatically, may subsequently be compressed isothermally. The gas compressor may further comprise fourth valve means operable after expansion in the second chamber of hot compressed gas introduced by the second valve means, to draw in additional low pressure gas before the velocity of the second piston in the direction out of the second chamber reaches zero. Thus, some of the kinetic energy imparted from the hot compressed gas is used to draw in an additional mass of gas into the second chamber before the gas is compressed.
In another embodiment, either with or without a second chamber, the means to deliver driving energy comprises further valve means operable to admit hot compressed gas into the first chamber to drive the piston out of the first chamber. In this embodiment, the same gas used to drive the piston out of the chamber in the first half of the cycle, is compressed in the chamber in the second half of the cycle. This embodiment may comprise means to convert the kinetic energy imparted by movement of the piston out of the chamber into kinetic energy to impart movement to the piston into the chamber to compress the gas. A second chamber and a second piston may be provided, the second chamber containing a body of gas which converts the kinetic energy imparted by the hot compressed gas introduced into the first chamber into kinetic energy to drive the piston back into the first chamber to compress the gas. Thus, as the second piston moves into the second chamber, the gas therein is compressed adiabatically and then subsequently expands adiabatically, driving the second piston out of the second chamber and the first piston into the first chamber. Alternatively, the compressor may comprise a second chamber having second, third and fourth valve means as mentioned above. The compressor may also include valve means, operable after expansion in the first chamber of hot compressed gas introduced by the further valve means, to draw in additional low pressure gas, before the velocity of the piston in the direction out of the chamber reaches zero.
Advantageously, if the hot compressed gas introduced alternately into the first and second chamber is expanded adiabatically, the thermal energy of the gas is conveniently converted into mechanical energy, e.g. the kinetic energy of the piston, so that an additional mass of gas can after each expansion, be admitted into each chamber as the free volume of the chamber increases. The piston then momentarily comes to rest in one of the chambers and its motion is reversed by the injection and expansion of hot compressed gas in the same chamber, driving the piston into the other chamber which compresses the gas at a much lower temperature than the initial temperature of the hot compressed gas previously introduced. Thus, a given mass of compressed gas is converted into a larger mass of compressed gas, whereby the additional mass is effectively provided by the thermal energy of the hot compressed gas introduced into the chamber.
In another embodiment, the means to deliver driving energy comprises means to provide a combustible fuel mixture in the second chamber, whereby combustion thereof imparts kinetic energy to the piston or other kinetic energy storage means. In another embodiment, the means to deliver driving energy comprises means to admit compressed gas into the second chamber and further means to form a spray of hot liquid to heat the gas in the second chamber. Alternatively, the means to deliver driving energy comprises means to admit a gas producing medium together with a reaction gas for gasification into the second chamber. In each of these embodiments the means to deliver driving energy may further include means to feed compressed gas from the first chamber into the second chamber. Advantageously, heat exchanger means may be arranged to preheat cool compressed gas from the first chamber with hot expanded gas from the second chamber. Some of the preheated compressed gas leaving the heat exchanger may be used to drive a gas turbine. Use of some of the cool compressed gas to drive a turbine is particularly beneficial, if more heat is available in the hot expanded gas leaving the second chamber than is needed to preheat the volume of cool compressed gas required to drive the compressor. The compressor may be designed to produce additional cool compressed gas to recover this excess heat. In this way, the surplus heat may be recovered so that it can be converted into useful power.
The compressor may comprise a third chamber to contain gas to be compressed and a third piston to compress the gas by movement of the third piston into the third chamber and include further valve means to allow compressed gas to be drawn from the third chamber. The third chamber and third piston may be arranged such that when the second piston moves out of the second chamber, the third piston moves into the third chamber. Thus, the processes which drive the second piston out of the second chamber may be used to drive the compression of gas in the third chamber. Where the compressor comprises a U-shaped conduit containing a liquid piston forming the first and second pistons, the third piston may be formed by, for example arranging the third chamber in the same arm of the conduit as the first chamber. A piston comprising a solid material may be arranged between the third piston and the third chamber. If a solid piston is also provided above the liquid piston in the first chamber, the solid pistons may be arranged to move independently of one another or connected together and, for example may comprise a unitary body. Where the first, second and third pistons all comprise a solid material, the pistons may be effectively formed as a unitary body and collectively serve to provide the kinetic energy storage means. The gas in the third chamber may be compressed adiabatically and the compressed gas may be used to drive a gas turbine. If a separate gas turbine is used to recover excess heat in the hot expanded gas from a process in the second chamber, exhaust gas from the separate turbine (which may be still relatively hot) may be used to preheat some of the cold compressed gas from the first chamber, for example in a heat exchanger, and this preheated compressed gas may be used to drive the gas turbine driven by adiabatically compressed gas from the third chamber. Alternatively, adiabatically compressed gas from the third chamber and preheated compressed gas used to recover excess heat from the exhaust gas, may both be directed to a single turbine, thereby advantageously avoiding the need for more than one turbine.
In an alternative arrangement, the second chamber and second piston may each be arranged such that on movement of the first and third pistons into a respective chamber, the second piston moves into the second chamber. A process in the second chamber then drives the first, second and third pistons out of their respective chambers imparting kinetic energy to the kinetic energy storage means, which may advantageously be the combined mass of the pistons. Means to convert the kinetic energy into kinetic energy to drive the pistons back into their respective chambers is provided and may comprise an adiabatic compression/expansion chamber, containing a body of gas, and an associated piston coupled to the other pistons so that on movement of the second piston out of the second chamber, the further piston moves into the adiabatic/expansion chamber.
In another embodiment, the second chamber and second piston are each arranged such that on movement of the first and third pistons into their respective chambers, the second piston moves out of the second chamber. The gas compressor may comprise a fourth chamber and a fourth piston each arranged such that on movement of the second piston into the second chamber, the fourth piston moves out of the fourth chamber. In addition to driving energy being delivered by a process in the second chamber to drive the first and third pistons into their respective chambers to compress the gas therein, a process including any of those mentioned above in connection with the second chamber may be arranged to occur in the fourth chamber to drive the second piston back into the second chamber, and consequently the first and third pistons out of their respective chambers.
The gas compressor may further comprise a fifth piston and a fifth chamber to contain gas to be compressed by movement of the fifth piston into the fifth chamber, the fifth piston and fifth chamber being arranged such that on movement of the second piston into the second chamber, the fifth piston moves into the fifth chamber and the compressor includes further valve means to allow compressed gas to be drawn from the fifth chamber. The fifth chamber may be used to compress gas adiabatically which may be subsequently used to drive a gas turbine which may be the same gas turbine driven by adiabatically compressed gas from the third chamber. The adiabatic compression in the fifth chamber is driven by a process in the fourth chamber.
Further, the compressor may comprise a sixth piston and a sixth chamber to contain gas to be compressed by movement of the sixth piston into the sixth chamber, the sixth piston and sixth chamber being arranged such that on movement of the second piston into the second chamber, the sixth piston moves into the sixth chamber, and the compressor comprises further means to form a spray of liquid in the sixth chamber to cool the gas on compression therein and further valve means to allow compressed gas to be drawn from the sixth chamber. The sixth chamber thus provides a second isothermal compression chamber to produce cool compressed gas. The isothermal compression in the sixth chamber is also driven by the process in the fourth chamber. Thus, in this form of the compressor, a process in the second chamber drives the isothermal and adiabatic compression processes in the first and third chamber, respectively, during one half of the cycle, and a process in the fourth chamber drives the adiabatic and isothermal compression processes in the fifth and sixth chambers, respectively, in the other half of the cycle. The means to deliver driving energy may further include means to feed compressed gas from the sixth chamber into the second and/or fourth chamber and may further include heat exchanger means to preheat compressed gas from the sixth chamber with gas from the second and/or fourth chamber. The heat exchanger means may comprise the same heat exchanger means arranged to preheat compressed gas from the first chamber with gas from the second chamber. Heat which is not required to preheat the cool compressed gas from the sixth chamber required to drive the process in the second and/or fourth chamber may be recovered by passing additional cool compressed gas from the first and/or sixth chambers through the heat exchanger means, whereupon the excess heat is used to preheat the additional compressed gas and then this gas may be used to drive a gas turbine. In any of the above embodiments, any two or more of the pistons may be arranged in tandem and for example, inter-connected by one or more sealed shafts passing from one chamber to the next. Alternatively, any two or more of the pistons may be spaced laterally relative to their direction of motion into and out of their respective chambers.
Where hot compressed gas is used to drive the compressor, the gas may be provided by a conventional mechanical compressor, or from cool compressed gas produced in the isothermal compressor itself which is then preheated with hot expanded gas from the second and/or fourth chambers by means of a heat exchanger, and which is then heated further in a main heater by for example combustion of fuel. In general, the resulting hot compressed gas will be at a much higher temperature than the gas produced by a mechanical compressor. The very hot compressed gas is then introduced into the second and/or fourth chamber in which it expands to drive the compressor. Advantageously, the hot compressed gas introduced into the second and/or fourth chamber drives the compressor by simple adiabatic expansion and is therefore a much cleaner process than either combustion or gasification.
In another embodiment, the compressor may comprise in addition to a first chamber and a second chamber, if there is one, a further chamber to contain gas to be compressed, a further piston to compress the gas by movement of the further piston into the further chamber, valve means to allow compressed gas to be drawn from the further chamber and means to feed compressed gas from the further chamber to the first and/or second chamber. The further piston is independent of the first piston and the compressor may comprise second kinetic energy storage means coupled to the further piston, and to which sufficient kinetic energy can be imparted to enable the further piston to compress the gas in the further chamber. The second kinetic energy storage means may comprise a mass arranged to move in phase with the further piston and the mass may conveniently be provided by the further piston. The gas contained in the further chamber is compressed adiabatically and may used to drive the isothermal compression process in the first chamber and the second chamber (if there is one). Adiabatically compressed gas may also be used to drive a gas turbine.
This form of the compressor may further comprise means to impart kinetic energy to the second kinetic energy storage means and may also comprise means to convert the kinetic energy used to impart movement to the further piston in one direction into kinetic energy to impart movement to the further piston in the other direction. The means to convert may include means to convert kinetic energy used to impart movement to the piston into potential energy, for example by providing a mass arranged displaced vertically on movement of the further piston, which may be provided by the mass of the further piston itself.
The compressor may also comprise a fourth chamber and a fourth piston each arranged such that on movement of the further piston into the further chamber, the fourth piston moves out of the fourth chamber, and the further and fourth pistons together may comprise a unitary body. Although in this embodiment there may not be a second chamber and a second piston the fourth chamber and fourth piston are so termed for the purpose of distinguishing one chamber and piston from another. The means to convert the kinetic energy used to impart movement to the further piston may include a body of gas contained in the fourth chamber, which is alternately compressed and allowed to expand adiabatically, to drive the further piston into the further chamber to compress the gas. This is particularly advantageous where the means to impart kinetic energy to the second kinetic energy storage means comprises a process in the further chamber. For example, the means to deliver driving energy to the further piston and impart kinetic energy to the second kinetic energy storage means may comprise means to provide a combustible fuel mixture in the further chamber, whereby combustion thereof imparts the kinetic energy. Alternatively, the means to impart kinetic energy to the second kinetic energy storage means may comprise means to admit compressed gas into the further chamber and further means forming a spray of hot liquid to heat the gas in the further chamber. In another embodiment, the means to deliver driving energy to the further piston comprises means to admit a gas producing medium together with a reaction gas for gasification into the further chamber and in another embodiment the means to deliver driving energy to the further piston may comprise valve means operable to admit hot compressed gas into the further chamber. Thus, in any of the above embodiments, the adiabatic compression in the further chamber is driven by a process which takes place in the same chamber. As a result of the process, hot gas in the further chamber expands and drives the further piston out of the further chamber. Valve means, operable after expansion of gas in the further chamber, may be provided to draw gas into the chamber which is subsequently to be compressed adiabatically. The valve means may be positioned so that the gas is drawn in directly above the piston. In this embodiment, the compressor further comprises valve means operable after induction of gas into the further chamber, to allow the hot expanded gas to be expelled from the chamber on movement of the piston into the further chamber. The valve means is operable, after expulsion of hot expanded gas from the chamber, to close to allow the gas drawn into the chamber after the expansion process to be compressed. The kinetic energy imparted to the second kinetic energy storage means by the process in the further chamber may be converted into kinetic energy to impart movement to the further piston into the further chamber by adiabatic compression and expansion of gas in the fourth chamber.
In another embodiment, the fourth chamber may incorporate any of the features described above in relation to the further chamber, so that a process in the fourth chamber drives the adiabatic compression in the further chamber and the process in the further chamber drives adiabatic compression in the fourth chamber. Advantageously, this embodiment produces adiabatically compressed gas twice during one complete operating cycle. The separation of the gas to be compressed adiabatically and the process gas in the further chamber and the fourth chamber is effected by natural thermal stratification.
In another embodiment, adiabatic compression and a process to drive the adiabatic compression may take place in separate chambers. Thus, adiabatic compression only may take place in the further chamber and the process to drive the adiabatic compression may take place in the fourth chamber.
In another embodiment, the fourth chamber and the fourth piston may each be arranged such that on movement of the further piston into the further chamber, the fourth piston moves into the fourth chamber. Henceforth, the further piston and further chamber will be referred to as the third piston and third chamber, respectively, although there may not be a second piston and a second chamber. Likewise, the terms fourth, fifth and sixth distinguish one piston or chamber from another although there may not be a second chamber. The compressor may further comprise a fifth chamber and a fifth piston, each arranged such that on movement of the third piston into the third chamber, the fifth piston moves out of the fifth chamber. In this embodiment, means to impart kinetic energy to the second kinetic energy storage means may comprise a process in the fourth chamber which drives the fifth piston into the fifth chamber. The fifth chamber may contain a body of gas which converts the kinetic energy into kinetic energy to impart movement to the fifth piston so as to drive the third piston into the third chamber to compress the gas contained therein.
In another embodiment, the gas compressor may comprise means to provide a process in the fifth chamber so as as impart kinetic energy to the second kinetic energy storage means, thereby to drive the further piston into the further chamber to compress the gas therein. Thus, the means to impart kinetic energy to the second kinetic energy storage means may comprise means to provide a combustible fuel mixture in the fifth chamber, whereby combustion thereof imparts the kinetic energy. Alternatively, the kinetic energy storage means may comprise means to admit compressed gas into the fifth chamber and further means to form a spray of hot liquid to heat the gas in the fifth chamber. In another embodiment, the means to impart kinetic energy to the second kinetic energy storage means may comprise means to admit a gas producing medium together with a reaction gas for gasification into the fifth chamber. In another embodiment, the means to impart kinetic energy to the second kinetic energy storage means may comprise valve means operable to admit hot compressed gas into the fifth chamber.
The gas compressor may further comprise a sixth chamber to contain gas to be compressed, a sixth piston arranged with the sixth chamber such that on movement of the fifth piston into the fifth chamber, the sixth piston moves into the sixth chamber and may further include valve means to allow compressed gas to be drawn from the sixth chamber. Thus, in this embodiment, adiabatic compression is performed in two chambers and the process to drive the compression is performed in two other chambers. The process in the fifth chamber drives the compression in the third chamber and the process in the fourth chamber drives the adiabatic compression in the sixth chamber. Thus, advantageously, the adiabatically compressed gas is kept completely separate from the process gas. Furthermore, this embodiment is symmetric and produces adiabatically compressed gas twice per cycle. The adiabatically compressed gas from each of the third chamber and sixth chamber may be used to drive the isothermal compression in the first chamber (and second chamber if any) and may also be used to drive a gas turbine.
In a preferred embodiment, the means to impart kinetic energy to the second kinetic energy storage means further comprises means to feed compressed from the first and/or second chamber to the third, fourth or fifth chambers, as required, to drive a process therein. Preferably, heat exchanger means are provided to preheat compressed gas from the first and/or second chamber with heat from the hot expanded process gas leaving any one of the third, fourth or fifth chambers.
In another embodiment of the compressor, energy required for isothermal compression may be provided by a reservoir of liquid. One form of a liquid driven gas compressor comprises a conduit and a further piston arranged within and to move along the conduit and to drive the first piston into the first chamber to compress the gas therein. A reservoir for containing liquid is connected at one end of the conduit and the compressor further includes a main flow valve operable to control flow of liquid from the reservoir into the conduit to drive the further piston along the conduit, and discharge valve means operable, after compression of gas in the first chamber, to allow liquid to discharge from the conduit. The further piston may comprise a liquid or solid piston or a combination of both and may be formed integrally with the first piston. The compressor may comprise a plurality of chambers to contain gas to be compressed and pistons to compress the gas in each chamber, each of the pistons driven independently by an associated further piston, each of which is driven along a separate conduit one end of which is connected to a common reservoir. Preferably, the compressor includes means to return liquid discharged through the or each valve discharge means to the reservoir and the means to return may comprise a pump. Where the compressor comprises a plurality of conduits and associated pistons driving compression processes in a plurality of chambers, the main flow valves and discharge valves may be timed to operate so that liquid is being returned to the reservoir at the same time as liquid is being discharged therefrom so that the inventory of the reservoir is maintained substantially constant. In a preferred embodiment, the compressor further comprises means to pressurize the liquid in the reservoir. The reservoir may comprise a chamber enclosing a body of pressurized gas above the liquid. Where the means to return liquid to the reservoir comprises a pump, it will be appreciated that by arranging the main flow valve means in each conduit to control the pistons to operate out of phase, the pump can operate continuously and at optimum efficiency, since it is required to continuously supply liquid to the reservoir.
Conveniently, where the compressor comprises a liquid piston, the compressor may include means to supply the or each spray forming means with liquid from the liquid piston as liquid in the spray.
Preferably, the compressor includes cooling means for cooling the liquid used in the spray. The compressor preferably also includes means for controlling the size of droplet in the spray. The spray forming means may include a pump timed to operate only while gas in the or each chamber is being compressed. The spray forming means is preferably arranged to provide a spray of constant flow rate while gas in the or each chamber is being compressed and the spray forming means may include a positive displacement pump.
One embodiment may include means to mechanically couple a piston to the spray pump. Advantageously, such mechanical coupling may facilitate the timing of spray liquid injection and allow transfer of mechanical power from the piston to the pump and vice versa. The mechanical coupling may comprise for example a crankshaft driven by the piston or a rack, connected to the piston and arranged to drive a pinion. Rotation of the crankshaft or pinion may be used to drive a rotary pump or may be translated into reciprocating motion to drive a reciprocating pump. In some embodiments spray liquid is expelled from the compression chamber with the compressed gas. Such liquid is at a relatively high pressure, and may be, for part of the cycle at a higher pressure than is required to inject the spray liquid into the chamber. In this case, the pump may produce positive power, which may be used to drive the piston. Alternatively, the compressor may be designed without a mechanical pump, the pressure for injecting the spray being provided by the piston itself. Alternatively, the pump may be driven electrically or by some other means. If the pump provides a net power output, then it may be appropriate to connect the pump to drive a generator.
In a preferred embodiment, the compressor includes means to extract liquid from the compressed gas drawn from the or each chamber, if any, and may comprise a moisture separator. Preferably, the compressor also includes means to feed liquid from the means to extract to the or each spray forming means. Thus, advantageously the spray liquid recovered after isothermal compression (or in some embodiments after isothermal expansion) is continuously recycled.
The compressor may include means for controlling any one or more of the valve means to open or to close depending on any one or more of a number of parameters such as the position of the piston in a respective chamber, the pressure of gas in one of the chambers, time dependency or when a predetermined mass or volume of gas has either left or entered a chamber. Such parameters may be measured or detected by sensors, which provide corresponding output signals used to control the valves, for example, hydraulically, electromagentically and/or mechanically. The sensor or sensors may be for example electromagnetic, inductive, capacitive, electrical contact, ultrasonic or piezoelectric. A microprocessor or other type of computer may be arranged to process and interpret output signals from the sensor(s).
In one embodiment, one or more of the valve means may be mechanically coupled to one or more pistons, so that the piston drives the valve means to open and/or to close. An appropriate mechanical coupling may be provided by a rack connected to the piston arranged to drive a pinion mounted, for example, on the wall or base of the chamber. The pinion may be arranged to rotate a cam or drive a camshaft which opens and/or closes one or more valves at the appropriate time.
Where the compressor includes a liquid piston, a float of solid material may be arranged to float on the surface of the liquid piston in at least one of the chambers. The float may be either rigid or flexible and is effective to suppress turbulance at the surface of the piston and entrainment of liquid into the gas above the liquid piston, both of which are potential loss mechanisms. Advantageously, the float may be made of porous material to facilitate the spray liquid to combine with the liquid in the liquid piston.
In some circumstances, cooling of the chamber walls is desirable, depending on the heat generated by the various processes occurring in the chambers. The chamber walls may be cooled by cool compressed gas from one or more of the isothermal compression chambers. The chamber walls, may have a plurality of holes formed therein so that the cooling gas, after taking up heat from the chamber walls, may pass into the chamber and expand with the other expanding gas in the chamber. Alternatively, the heated compressed cooling gas may be passed to and expanded in a turbine. Advantageously, either method enables excess heat to be recovered from the chamber walls in such a way as to be convertable into useful mechanical power.
Where the compressor includes heat exchanger means to cool the exhaust gas from a process in one of the chambers with cool compressed gas from the isothermal compression chamber, it may be desirable to provide moisture removing means to remove liquid from the cool exhaust gas leaving the heat exchanger means. Such an arrangement may include second heat exchanger means to cool the exhaust gas from the first heat exchanger means, means to remove moisture from the cooler exhaust gas leaving the second heat exchanger means, a cooler to reduce the temperature of the cooler exhaust gas leaving the moisture removing means, second moisture removing means to remove moisture from the cold gas leaving the cooler and means to feed the cold exhaust gas from the second moisture removing means to the second heat exchanger in which it is heated with the cool exhaust gas leaving the first heat exchanger.
Another aspect of the invention provides a gas turbine plant comprising a gas turbine, an isothermal compressor producing cold compressed gas, means to preheat the cold compressed gas, a main heater to generate hot high pressure gas from the preheated compressed gas and means to feed the hot high pressure gas to drive the turbine. Preferably, the means to preheat comprises a heat exchanger arranged to preheat the cold compressed gas from hot low pressure gas leaving the gas turbine.
In one embodiment of this aspect of the present invention, the main heater comprises a combustion chamber burning fuel in the preheated pressurized gas and producing combustion gas as the hot high pressure gas.
In another embodiment of this aspect of the present invention, the main heater comprises an external source of heat. This external source of heat may be for example a coal or oil fired furnace, a chemical or industrial process, a nculear reactor or a solar furnace.
Advantageously, the gas turbine plant may include means for feeding part of the cold compressed gas to the gas turbine blades for cooling thereof. This enables any upper limit of the temperature inside the turbine set by the turbine blades to be increased.
In one embodiment, the gas turbine plant may include a further gas turbine and means for feeding part of the hot compressed gas from the heat exchanger to drive the further gas turbine. This is especially advantageous when the heat exchanger exchanges heat between a cooler gas having a higher specific heat and a hotter gas having a lower specific heat, so that not all the heat in the hotter gas is need to raise the temperature of the cooler gas. The residual heat can conveniently be used to heat part of the cool gas from the compressor to drive a further gas turbine.
The above embodiments may further include a third gas turbine, a second heat exchanger to preheat part of the cold compressed gas from hot low pressure gas leaving the further gas turbine and means to feed the preheated gas to drive the third gas turbine. Preferably, the isothermal compressor is driven by one of the gas turbines. The isothermal compressor may comprise the gas compressor or any embodiments thereof mentioned above.
In another embodiment of this aspect of the present invention, the gas turbine plant may further include a vessel for storing cold compressed gas from the isothermal compressor and means for recovering the stored compressed gas for driving the turbine when required.
According to another aspect of the present invention, there is provided an energy storage plant comprising an isothermal gas compressor as described and claimed, a storage vessel for storing cold compressed gas from the compressor and means to feed gas from the compressor to the storage vessel.
Preferably the energy storage plant includes an isothermal expander comprising a chamber to contain gas to be expanded, a piston to allow the gas to expand by movement of the piston out of the chamber, means to form a spray of liquid in the chamber to heat the gas on expansion therein, and valve means to admit compressed gas into the chamber from the storage vessel. The isothermal expander may further comprise a second chamber to contain gas to be compressed by movement of the piston into the second chamber, and valve means to allow compressed gas to be drawn from the second chamber. Advantageously, the hot compressed gas, which may be air, may be used to drive a gas turbine.
The gas compressor according to various aspects of the present invention, may be driven in reverse as an isothermal gas expander, the difference being that cool compressed gas is introduced into the chamber and allowed to expand by movement of the piston out of the chamber, and the means to form a spray of liquid in the chamber transfers heat to the gas during expansion so that the expansion may be approximately isothermal. The energy imparted to or via the piston may be used to compress the expanded gas in the chamber adiabatically or if there is a second chamber, to compress gas in the second chamber adiabatically. The adiabatically compressed gas may then be used to drive a gas turbine, for example an air turbine. Thus, the gas compressor/expander provides a means of converting cold compressed gas stored in a storage vessel into useful power.
According to another aspect of the present invention, there is provided a gas compressor comprising a chamber to contain gas to be compressed, a piston to compress the gas by movement of the piston into the chamber, valve means to allow compressed gas to be drawn from the chamber, wherein the mass of the piston is sufficient to enable all the energy required to compress the gas to be stored in the piston.
Kinetic energy would normally be imparted to the piston by some process which involves the expansion of gas. The energy released in the process may continuously vary over time. Advantageously, by providing a massive piston, all the energy released during the process is transferred to kinetic energy of the piston. Furthermore, because the piston is sufficiently massive to store the kinetic energy released by the process, a fly wheel is not required which removes the need for mechanical linkages and couplings which are susceptible to wear.
According to another aspect of the present invention, there is provided a gas compressor comprising a piston, means forming a chamber to contain gas to be compressed and to compress the gas by movement of the chamber over the piston, means to form a spray of liquid in the chamber to cool the gas on compression therein and valve means to allow compressed gas to be drawn from the chamber. In this aspect of the present invention, the piston is arranged to remain stationary relative to the movement of the chamber. As will be appreciated by those skilled in the art, the various embodiments described in relation to a compressor comprising a moveable piston and a stationary chamber may be modified, mutatis mutandis, so that motion is imparted to the or each chamber and the piston remains stationary.
The terms xe2x80x9chotxe2x80x9d or xe2x80x9ccoolxe2x80x9d or xe2x80x9ccoldxe2x80x9d used throughout the specification and claims are used in a relative sense to distinguish that which is at a higher temperature from that which is at a lower temperature and are not intended to limit the temperatures to any particular value or range. Thus, the term hot includes temperatures which may normally be considered cold, and the term cold includes temperatures which may normally be considered hot.